Microbiology- Exam 1

The International Committee on the Taxonomy of Viruses uses the following criteria to classify viruses EXCEPT i. capside symmetry ii. the size of the viral particle iii. genome composition iiiii. mRNA type

iiii. mRNA type

Sort the following microbial processes to identify which will likely be impacted when a patient is treated with rifampicin and which will not.

impacted by: transcription replication translation likely not impacted by: transduction lysogeny

A bacterial species is discovered that contains thylakoids and carboxysomes. It can be assumed from the presence of these structures that this bacterium

is capable of photosynthesis

Coupled transport to move nutrients into the cell against their concentration gradients is most likely to occur as the electrical gradient moves

positive ions into the cell

Virus phylogeny based on proteomics is

possible because viruses encode a small number of proteins.

Which of the following is not a mechanism by which plasmids ensure their inheritance and maintenance during cell division?

low-copy-number plasmids

Cholera autoinducer (CAI-1) allows the bioluminescent bacterium Vibrio harveyi to sense the presence of

other Vibrio species.

The lipopolysaccharides are found in the

outer membrane

Certain aquatic bacteria use magnetosomes to direct them to environments with optimal levels of ________

oxygen

In E. coli, the sigma S regulon is important for cellular responses to which of the following?

pH extremes nutrient depletion oxidative stress

In some cases, a set of objective lenses on a microscope can be interchanged without losing good focus of a specimen. The term used to describe this is

parfocal

Which one of the following proteins would be found in the outer membrane of Gram-negative bacteria?

peptide porins

The bacterial cell wall is composed mainly of

peptidoglycan

Which of the following modifications would likely cause constitutive expression of a gene that is normally regulated by an activator protein?

replacing the promoter with the consensus sequence for RpoD σ70

Unlike primary chromosomes, secondary chromosomes in bacteria have which quality?

replication using plasmid-like molecular mechanisms

Proteins destined for the bacterial cell membrane

require the activity of SRP.

Why were marine viruses overlooked for so many years?

researchers tried to isolate marine viruses using non-marine host cells

While horizontal gene transfer can be beneficial, there are also risks. Bacteria protect themselves from foreign DNA through

restriction endonucleases that cleave unmethylated DNA at specific sites.

Association of RecA with an incoming piece of foreign DNA is required for a cell to do which of the following?

swap the incoming DNA with a homologous region on the chromosome

Crop rotation (alternating planting of grains and legumes) has been practiced for thousands of years, long before anyone understood the contribution of ______ to enhancing soil fertility

symbiotic

Pathogenicity islands (PAIs) are often found integrated near

tRNA genes

RNA comes in many forms in the cell, and their structure and longevity are determined by their function. Which of the following has the longest half-life?

tRNA—shuttles amino acids during translation

V. cholerae is capable of transformation, which means it can do what?

take up naked DNA

In bacterial cells,

transcription, translation, and DNA replication can all occur at the same time in the same cell compartment.

Which of the following would not be included in the formulation of a defined medium?

tryptone

The bacterial cytoskeletal proteins FtsZ and MreB are homologous to the eukaryotic __________ and __________, respectively.

tubulin; actin

Which of the following would be the best electromagnetic energy to use to get the greatest resolution of a bacterial cell?

ultraviolet

A bacterial cell that lacked the Rho protein would be

unable to terminate transcription of some genes.

Which class of molecules can directly cross the cell membrane without the aid of transport proteins?

uncharged gasses

For a Gram-negative bacterium such Escherichia coli, the four major destinations for extracytoplasmic proteins (proteins not in the cytoplasm) are the plasma membrane, extracellular spaces, the outer membrane, and the _______

periplasm

a prophage is a

phage genome integrated into a host genome.

Visualization techniques that rely on interference effects are

phase-contrast microscopy and x-ray crystallography

Metagenomic analyses have demonstrated that the composition of the intestinal microbiota can influence susceptibility to all of the following human diseases and disorders, except which one?

phenylketonuria (PKU), which affects how the body processes proteins from food

What functional group do kinases transfer to other molecules as signals of environmental change?

phosphate

In the marine environment, which types of organisms form the base of the food chain?

photoautotrophic microorganisms

Which viruses enter cells via mechanical transmission, a nonspecific access through physical damage?

plant viruses

The plasmid encoded ParR and ParM proteins are involved in

plasmid partitioning.

Differential interference contrast microscopy uses

polarized light to produce multiple images that are superimposed and produce interference, highlighting differences in the refractive index of different parts of the cell, producing a false 3D effect.

Clostridium difficile is a common and serious infectious agent that causes severe intestinal distress. When cells of C. difficile are Gram-stained, they appear as Gram-___________rods, which are _______________in color and belong to the phylum of bacteria known as __________________.

positive purple Firmicutes

What is the correct temporal sequence for factors binding to an mRNA in bacterial translation initiation?

30S ribosomal subunit, N-formylmethionine-tRNA, 50S subunit

If a bacterium can divide once an hour, then after 5 hours, 1 bacterium will have yielded __________ bacteria.

32

Analysis of the genome of a newly discovered bacterial strain reveals that it is composed of a double-stranded DNA molecule containing 16% thymine. Based on this information, what would you predict the percentage of cytosine to be?

34%

E. coli DNA polymerase III has which of the following activities?

3′ to 5′ exonuclease

During DNA replication, each new nucleotide adds on to the hydroxyl group on the

3′-C of the sugar.

If a segment of RNA reads 5′ GCCUUAA 3′, then the corresponding DNA template strand reads

5′ TTAAGGC 3′.

If an organism has a mean growth rate constant (k) of 1/hour, then the mean generation time, g, is

60 minutes

A food worker was preparing some macaroni salad on the same counter on which he had cut up some raw chicken. Suppose this resulted in the accidental introduction of 380 cells of E. coli into the 1 gallon container of macaroni. This careless worker then left it unrefrigerated until 6 hours later. Now consider that E. coli has a doubling (generation) time of 20 minutes when grown in a rich medium. Assuming the cells were dividing at their maximum rate in the macaroni salad, what would the level of bacterial contamination be by the time it was finally refrigerated?

9.96 x 10^7 cells

Which of the following conditions may lead to a switch from a lysogenic to a lytic life cycle?

A dearth of glucose in the environment

For an acid-loving microbe (acidophile) living in an acidic environment in the presence of both penicillin and tetracycline, which of the following will end up crossing into the cell and impacting the internal cytoplasmic pH?

form B of penicillin

The AraC-like regulators differ from the LacI repressor in that only the AraC-like regulators

can activate transcription by direct interactions with RNA polymerase.

oxygen

can be used as a terminal electron acceptor by microbes capable of cellular respiration, thereby generating more energy than other pathways.

Nitrogen-fixing bacteria

can convert atmospheric nitrogen into ammonium ions.

Chemical disinfectants

can damage macromolecules in a microbial cell.

a temperate phage is one that

can undergo lysogeny.

a gene for a ____ is likely to be encoded in the viral genome

capsid protein

During base excision repair, a specific glycosylase catalyses

formation of AP site

A secondary chromosome is distinguished from a plasmid because it

carries one or more essential genes.

Which of the following requires a protein?

formation of hydrogen peroxide from a superoxide radical

The invention of the ultracentrifuge led to rapid advances in cell biology by allowing scientists to do which of the following?

fractionate subcellular parts

Cis-antisense RNA (asRNA) differs from regulatory small RNA (sRNA) in its ability to

cause premature transcription termination of mRNA.

Fixation and stained preparation of specimens

causes cells to stay in one place and improves contrast as well as usually imparts color, improving detection.

The cell structure immediately external to the cytoplasm is the

cell membrane

Penicillin's mode of action is to inhibit

cell wall cross-link formation

One technique used to separate cell components is

centrifugation

Which of the following elements must be present for attenuation of the trp operon to occur? Select all that apply.

charged tRNATrp ribosomes RNA polymerase

Some bacteria live in deep sea vents where no light penetrates, yet are still capable of producing their own reduced carbon. These organisms are classified as

chemoautotrophs

Cells of a normally rod-shaped bacterium (e.g., Bacillus subtilis) that have completely lost the ability to produce the MreB protein would mostly likely be

coccoid-shaped.

the phenol _____ is used to compare the maximum effective dilution of a test substance to the maximum effective dilution of phenol to determine the test substance's relative effectiveness in killing microbes.

coefficient

crystal violet

complexes with iodide ions, producing a positively charged molecule that stays more strongly within the peptidoglycan cell wall.

bacterial genomes

depend on the species

Compared to wild-type E. coli, a mutant with overactive RelA would be expected to have

fewer ribosomes in exponential phase.

Transposases are multifunctional enzymes. During nonreplicative transposition, the transposase does all of the following except

fill in single-stranded gaps that occur in the target region of the recipient DNA.

Endosymbionts in plants

fix nitrogen needed for proteins and nucleic acids

Investigators have determined that high intracellular levels of c-di-GMP inhibit invasion of Salmonella into colonic epithelial cells. These results suggest that production of _____ is required for entry of Salmonella into host cells

flagella

One method for counting only the cells that express a particular protein on their cell surface is

fluorescent activated cell sorting (FACS).

What type of mutation is most likely to occur as a result of nonhomologous end joining repair?

frameshift mutation

Chaperones that maintain protein shape and enzymes that change membrane lipid composition are produced during the

heat-shock response

Most tRNAs become charged with

an amino acid

Suppose you have isolated a compound that alters the quorum signal of Pseudomonas aeruginosa, such that it cannot interact with its normal receptor. Bacterial cells targeted by such a disrupter would most likely

be similar to free-living cells in their sensitivity to antibiotics.

Why is ATP hydrolysis required for these transporters to operate properly?

because it causes a conformational change to open the channel to the other side

Concerning the RNA polymerase holoenzyme, which of the following are the core subunits or factors needed for transcription?

beta subunit alpha subunit beta-prime subunit

Barophilic prokaryotes are found primarily

deep in the ocean.

Siderophores are responsible for helping bacteria acquire

iron

The presence of hydroxyl radicals indicates that the cell likely has which of the following?

iron

Which of the following best describes the unusual image alterations that occur when using differential interference contrast microscopy?

"false 3D" effect

New and emerging viruses come from

"jumping" hosts

Which viral genome is likely to require an RNA-dependent RNA polymerase for transciption upon viral entry?

(-) sense single-stranded RNA

Identify which organisms can be infected by viruses. Bacteria Plants Animals Archaea Algae Fungi Protists

(ALL) Bacteria Plants Animals Archaea Algae Fungi Protists

A piece of double stranded DNA is 800 kb. The number of individual nucleotides in this piece of DNA is ________ bases.

1,600,000

DNA mismatch repair is the primary mechanism for correcting misinserted base pairs caused by

DNA polymerase.

A Gram-negative cell envelope contains

an inner cell membrane, thin peptidoglycan layer, and outer membrane.

Order the following events as they occur from beginning to end during DNA replication in a dividing cell.

1. DNA at origin unzips, and two replication forks form 2. replisomes synthesize daughter chromosomes bidirectionally 3. terminator site is replicated 4. septum forms 5. daughter cells separate

Correctly order the following steps in bacterial conjugation from start to finish.

1. sex pillus formed that joins an F+ cell to an F- cell 2. sex pilus retracts and a relaxosome forms 3. the F factor is nicked at oriT, and one strand starts to transfer to recipient 4. DNA polymerase 3 synthesizes a replacement strand in the donor 5. The transferred DNA is not required for normal cellular function.

place in order

1. sterilize the loop (and allow it to cool) before using it to obtain the bacterial inoculum 2. remove a sample of bacteria from the culture flask (or plate) using the sterile loop 3. inoculate a section of you agar petri dish by sweeping the loop back and forth across the surface 4. flame and loop a second time and allow to cool 5. using the loop, streak cells fro the first area onto a fresh section of agar 6. flame the loop a third time and allow it to cool 7. using the loop, draw cells from the second area onto another fresh section of agar 8. sterilize the loop a final time 9. place the petri plate in the appropriate incubator

A nanometer, nm, is equal to _____ meters.

10^-9

In gene translation, one can think of a kind of "punctuation" that is used to represent different aspects of making a protein. The beginning of the gene "sentence" (start) can be thought of as a capital letter used to represent the beginning of a written sentence. Similarly, the end of a sentence (stop) can be thought of as a period. Keeping this in mind, there would be ____ different combination(s) of codons that could be punctuate gene "sentences"

12

the average amino acid length of proteins in Escherichia coli is 235. Therefore, according to the video, the elongation time for an average E. coli protein would be about ____ seconds

15

The resolution of the human retina is

150μm

What is the name of the gene that was used as a "molecular clock" to classify archaea?

16S rRNA

Which statement best summarizes the types of genes analyzed and the purposes of those analyses in this large study?

16S rRNA genes were analyzed to identify phyla, while all other genes were analyzed to identify functional categories.

Amino-acyl-tRNA synthetases charge tRNAs with their respective amino acids. There are ________ amino-acyl-tRNA synthetases in a given cell.

20

Under optimal conditions, one E. coli cell can become two cells every

20 to 30 minutes

According to the video, it would take _____ GTP molecules to synthesize a protein 100 amino acids in length

200

When intracellular levels of tryptophan are low, the _________ stem loop forms, which results in ___________ of transcription.

2:3 / progression

Without base excision repair, the presence of unnatural bases may cause mutations or more serious effects. For example, the presence of ____ interferes with DNA synthesis, and is thus lethal to the cell

3-methyladenine

In bacteria, a partially diploid strain may result from

A.specialized transduction. B.acquisition of an F' factor.

The FepCGD complex is a type of

ABC transporter

Which of the following DNA molecules would most likely have the highest denaturing temperature (melting temperature, Tm)? Only a single strand of the double-stranded DNA is shown.

ACGGTGACGGCGCGAGCGC

Degradation of proteins in bacteria involves

ATP-dependent endoproteases.

Isoniazid inhibits mycolic acid synthesis and is a first-line antibiotic used to treat tuberculosis. How would you predict accelerators and alternators might vary in their sensitivity to this drug?

Accelerators should be more sensitive than alternators.

which of the following statements is true

All organisms require carbon as a macronutrient.

As temperatures drop, membrane fluidity decreases. Which of the following changes to phospholipids will help maintain correct bacterial membrane fluidity under cold temperatures?

An increase in unsaturated fatty acids

Which of the following is a difference between antiseptics and antibiotics?

Antibiotics can be taken internally but antiseptics cannot.

The first person to visualize a microbe was

Antoine van Leeuwenhoek.

How would removing the operator region from the E. coli tryptophan operon affect transcription of the trp genes?

B. Transcription of the operon would occur even if tryptophan were abundant.

Which of the following is true of complex media?

Bacteria grow faster on complex media than on synthetic media.

Sort each of the following features of Archaea transcription according to whether it more closely resembles that of Bacteria, Eurkarya, or both.

Bacteria: transcription termination amount of posttranscriptional processing many operons Eukarya: transcription initiation overall structure of RNA polymerase Both: nucleotides used

Why do bacteria usually contain an even number of replisomes?

Because replication is bidirectional, there are two replication forks emanating from the origin of replication.

Sort the following events according to whether they occur in replicative transposition, nonreplicative transposition, or both:

Both: DNA polymerase fills in gaps. Transposase is required. Target sequence gets duplicated. DNA ligase seals nicks. Nonreplicative : Hairpin structures form on each end of insertion sequence. Insertion sequence "jumps" into recipient DNA. Donor DNA loses insertion sequence. Replicative: Donor DNA retains a copy of insertion sequence. Recombination separates donor and target DNAs.

What two conditions must be met to produce a heritable mutation?

C.There is a change in the DNA sequence. D.The mutation does not get repaired before the cell divides.

Most organisms (including you) break down organic compounds to obtain energy and nutritional building blocks. In contrast, chemolithotrophs are prokaryotes that obtain energy through the oxidation of inorganic compounds. Which of the following inorganic molecules would these microbes also need to build macromolecules for new cell material?

CO2

Place the steps in the order which they occur during induction of bioluminescence in Allivibrio fischeri (referred to as Vibrio fischeri in the video; it has since been reclassified).

Cells produce AI, which diffuses across the membrane AI accumulates in extracellular environment AI diffuses into cell and combines with LuxR LuxR-AI binds to regulatory region of the lux operon luxAB genes are transcribed luciferase catalyzes luminescent reaction

Which of the following is true of cells in batch culture?

Cells will not remain at a constant mass.

DnaK, GroEL, and GroES are which kind of proteins?

Chaperonins

What is the difference between how class I aminoacyl-tRNA synthetases and class II aminoacyl-tRNA synthetases work, and what would have to be done at the end to produce similarly charged tRNA molecules?

Class I synthetases join the carboxyl group of the amino acid to the 2' OH of the tRNA and then the amino acid has to be moved to the 3' OH, whereas class II synthetases attach at the 3' OH, which is ready to be used directly.

Which of the following contains a large lactone ring and binds to the L15 protein and 23S RNA at the peptidyltransferase cavity to prevent peptide bond formation?

Erythromycin

If the adjacent tryptophan codons in the trp operon leader sequence are mutated to alanine codons, what is the predicted effect on trp operon regulation?

D. Attenuation may occur in response to high alanine levels. E. Attenuation will no longer occur in response to high tryptophan levels.

Identify the three domains of life according to the classification system developed by Carl Woese. Eukarya Archaea Prokarya Bacteria Viruses

Eukarya Archaea Bacteria

reverse transcriptase catalyzes ____ production from a _____ template

DNA RNA

Which enzyme helps pack DNA into the cell by negatively supercoiling DNA?

DNA gyrase

Gut bacteriophages, or "coliphages," are members of a microbial community that modulates human digestion, the immunesystem, and mental health. Historically, bacteriophages have provided some of the most fundamental insights in molecular biology. In 1952, Alfred Hershey and Martha Chase demonstrated that the transmission of DNA by a bacteriophage to a host cell led to the production of progeny bacteriophages. The discovery by Hershey and Chase confirmed that

DNA is the hereditary material of life.

Which of the following enzymes is used in methyl mismatch repair, nucleotide excision repair, and base excision repair?

DNA polymerase I

Which of the following situations is most important and likely to occur due to the Antarctic conditions?

DNA repair of thymine dimers and double-stranded breaks due to the cold and light

Recall the experiment mentioned in the chapter that addressed global warming effects on microbes. Using an infrared light, the team warmed a patch of Oklahoma prairie soil 2°C above that of an adjacent control patch of soil. The warming was done using an infrared light, and the microbes were analyzed by _____

DNA-based

Which of the following is the enzyme complex that catalyzes transcription in bacterial cells?

DNA-dependent RNA polymerase

Match each genome with the first polymerase it uses to initiate viral synthesis

DNA: double-stranded DNA single-stranded DNA Host RNA: (+) sense single-stranded RNA vRNA: double-stranded RNA (-) sense single-stranded RNA Reverse: (+) strand RNA retroviruses double-stranded DNA pararetrovir uses

Which of the following best explains why electron microscopes provide a much more detailed image of specimens than light microscopes?

Electrons have much shorter wavelengths than visible light waves.

Which of the following is true of endospores?

Endospores are resistant to many stresses that would kill vegetative cells.

Decide whether each enzyme is needed for typical prokaryotic chromosome replication only, typical eukaryotic chromosome replication only, or for replication of both chromosome types.

Eukaryotic Only: telomerase prokaryotic only: topoisomerase IV Both cell types: DNA primase DNA polymerase ligase helicase

Sort the following as either unique to eukaryotic regulation of transcription initiation or characteristic of all domains.

Eukaryotic Only: Mediator enhancers nucleosomes All Domains: activators repressors

Which of the following does NOT cause mutations?

Exposure to antibiotics

Upon successful completion of conjugation, the donor cell is ______ and the recipient cell is _____

F+,F+

How does flash-freezing the samples examined by cryo-EM improve the resolution of the resulting images?

Flash-freezing retains water in the sample but eliminates ice crystals.

Match each of the following microbiologists to a significant contribution to the field of microbiology. Fleming Ivanovsky Koch Jenner Semmelweis

Fleming: discovered that the Penicillium mold generates a substance that kills bacteria Ivanovsky: discovered viruses as filterable infective particles Koch: devised techniques of pure culture to study a single species of microbe in isolation Jenner: established the practice of vaccination (inoculation with cowpox to prevent smallpox) Semmelweis: showed that antiseptics could prevent transmission of pathogens from doctor to patient

Put the following steps in the correct sequence as they occur during flagellar synthesis in Salmonella.

FlgM binds to FliA FliA delivers FlgM to falgellar basal body FlgM is transported through the secretion channel FliA combines with RNA core polymerase to form holoenzyme Flagellin and motor protein genes are expressed

The energy used directly for the elongation step of translation comes from

GTP hydrolysis.

Scientists are continuously advancing our understanding of the importance of the human gut microbiome in health and disease. Which of the following is not a challenge associated with studying the human microbiome?

Genomic sequencing of the gut microbiome cannot be completed if the microorganisms cannot be cultured in the lab.

If a cytosine deaminates and becomes a uracil, which enzyme will cleave the uracil from the DNA backbone in the first step of a repair process?

Glycosylase

What controls the entrance to the chamber of chaperone protein GroEL?

GroES

Outline the correct sequence of steps to verify the predicted function of a gene from an uncultured organism.

I. DNA is sequenced to identify gene of interest II. the gene is inserted into a culturable organism III. the gene is transcribed IV. mRNA is translated V. the protein is purified VI. the protein is tested for predicted function

Which of the following are characteristic of a vegetative cell, endospore, or both?

I. Vegetative cell uses central septation site transcriptionally active binary division metabolically active II. Endospore dipicolinic acid small acid soluble proteins (SASPs) souble membrane resistant to heat, UV light, desiccation, etc. III. both chromosome proteins ribosomes peptidoglycan

The human intestinal tract has been likened to a culture vessel. The most commonly used lab culture systems include batch culture (growth in a test tube or flask) and chemostats. Sort the following list of features into the appropriate categories depending on whether they are characteristic of a batch culture, the gut tract, a chemostat, or gut and chemostat.

I. gut tract mixed species sporadic nutrient input fluid absorbed during culture II. chemostat continuous nutrient input continuous removal of cells and fluid III. batch culture one-time supply of nutrients defined death phase cells do not exist bacterial numbers change throughout IV. Gut & bacterial numbers remain relatively constant nutrients entering are balanced by wastes exciting

Sort the following methods of microbial protection against osmotic stress as to being either a common (housekeeping) method or used only in extreme conditions or not typically used at all.

I. house keeping diffusion of water across the membrane aquaporins allowing water molecules to move across the membrane increasing intracellular levels of compatible solutes mechanosensitive channels allowing solutes out of the cell II. extreme situations increased chaperone protein synthesis outer membrane pore composition changes III. not a mechanism diffusion of solutes across the membrane aquaporins allowing solutes to move across the membrane increased saturated fatty acids in membrane phospholipids mechanosensitive channels allowing water into the cell

Which of the following is the major difference between light microscopy and dark-field microscopy?

In dark-field microscopy, only scattered light enters the objective lens.

Antibiotics that weaken the peptidoglycan cell wall make a bacterium more prone to

osmotic lysis.

What is the role of dipicolinic acid in endospore formation?

It aids in dehydration of the endospore and enhances heat resistance.

Which of the following statements regarding transcriptional attenuation is true?

It allows the cell to respond rapidly to fluctuating levels of metabolites (e.g., amino acids).

What is the role of the first structural gene (lacZ) in the lac operon? Select all that apply.

It breaks down lactose into glucose and galactose. It isomerizes lactose into allolactose.

How does the cell membrane affect osmolarity?

It is semipermeable, allowing water molecules to move across while tending to keep solutes in (or out).

Which of the following statements is NOT true of sporulation?

It represents an important form of reproduction for some bacterial species.

Which scientist contributed to disproving spontaneous generation?

John Tyndall (and Pasteur)

One reason most organisms cannot grow at high temperatures is that

proteins denature

The discovery of which cycle is regarded as one of the major milestones in understanding cellular metabolism?

Krebs cycle

Which of these two probiotic microbes have been used to treat intestinal distress in children?

Lactobacillus and Bifidobacterium

Rank the following microorganisms from largest to smallest in size.

Largest Pelomyxa- Ameba found in soil Spirogyra- Aquatic algae Escherichia coli- bacteria found in human colon Prochloroccocus- photosynthetic marine bacteria Varicella- zoster virus- the virus that causes chickenpox Smallest

Which of the following cellular components is considered an endotoxin that is harmless as long as the pathogen remains intact but when released by a lysed cell overstimulates host defenses, which may result in a lethal endotoxic shock?

Lipopolysaccharides

The person who introduced vaccination into Europe was

Mary Montagu.

In response to extreme starvation, some bacterial cells undergo programmed cell death (PCD). In E. coli, PCD is mediated by the toxin-antitoxin pair MazF (the toxin that initiates PCD) and MazE (the antitoxin that keeps MazF in check). PCD lowers the fitness of the bacterial cell, but if the cells in the population are genetically related, then the sacrifice of some cells to keep a subset of the population alive may increase the fitness of that shared genome. There is, however, the risk of mutant "cheaters," cells that do not undergo PCD in response to extreme stress but benefit from the nutrients released from dead cells. Loss of which proteins could result in a cheater cell phenotype?

MazF ClpAP protease

As an up-and-coming scientist, you decide to create mutant bacteriophages to better examine structural function. Your first mutant lacks a sheath motor protein, so you decide to call this MutS. To determine the loss of function, you add MutS at a multiplicity of infection (MOI) of 1 to Escherichia coli cells and examine the rate of infection. You're very surprised to find that none of the Escherichia coli cells are infected. What happened?

MutS prevented the sheath protein from contracting.

A bacterial cell is infected by a phage with an RNA genome. The bacteria has not encountered this phage before. Which of the following correctly describes host defense mechanisms that can help protect the bacterial cell?

Neither CRISPR nor restriction endonucleases can provide defense.

Match each of the following scientists with his or her major contribution to microbiology. Nightingale Hooke Spallanzani Pasteur Tyndall

Nightingale: statistically quantified the impact of infectious disease on human populations Hooke: the first to record observations of microbes through simple microscopes Spallanzani: showed that microbes arise from preexisting microbes and that heat sterilization can prevent microbial growth Pasteur: discovered the microbial basis of fermentation and showed that providing oxygen does not enable spontaneous generation Tyndall: showed that repeated cycles of heat were necessary to eliminate spores formed by certain kinds of bacteria

Do Prochlorococcus have longer-living mRNA molecules than the mRNA of more rapidly growing microbes like E. coli?

No, Prochlorococcus mRNA also has short half-lives, very similar to half-lives of E. coli mRNA.

which statement about DNA vs. RNA is true

Only RNA contains a hydroxyl group on the 2′-carbon of ribose.

It is essential that sister chromosomes avoid the septum formation at the midline of the cell during bacterial cell division in order to prevent septal "guillotining" of chromosomes. Which of the following is not directly involved in the mechanism to prevent septal guillotining of chromosomes?

ParC

How do Phaeobacter compete for limited resources in the coastal salt marshes?

Phaeobacter secrete the compound indigoidine that kills other bacteria.

The cytoplasmic membrane is another cell component that is sensitive to pressure. How does pressure alter cell membranes, and how do barophiles adapt?

Pressure makes cell membranes less fluid. Barophiles adapt by using high levels of polyunsaturated fatty acids.

How did Prochlorococcus now living in the upper euphotic zone acquire the ability to repair their UV-damaged DNA?

Prochlorococcus likely acquired the photolyase genes through horizontal gene transfer.

Classify each of the following groups of organisms as prokaryotes or eukaryotes by dragging the items into the correct category. Bacteria Plants Animals Archaea Algae Fungi Protists

Prokaryotes: Bacteria Archaea Eukaryotes: Plants Animals Algae Fungi Protists

Sort the following chromosome characteristics based on whether they describe eukaryotic or prokaryotic chromosomes.

Prokaryotic Termination zones (ter sites) Operons NucleoidsCircular or linear chromosomes Eukaryotic Histones Telomeres Nucleus All linear chromosomes

How does R. palustris generate sufficient energy to make these repairs without carbon or nitrogen sources?

R. palustris uses photosynthesis to generate a membrane potential that is then used to generate ATP for protein synthesis and DNA repair.

What is the correct order of events in producing RNA-seq data?

RNA extraction, removal of stable RNAs, fragmentation of remaining RNAs, conversion to cDNA, sequencing, alignment to genome position, tabulation of number of fragments at each gene

The enzyme DNA primase is a(n)

RNA polymerase.

While plasmid replication is not tied to chromosomal replication, many of the proteins used for plasmid replication are host enzymes. Each plasmid contains its own origin of replication (ori) and only the few genes needed for replication. Which of the following proteins is needed for the rolling-circle mechanism of plasmid replication and is encoded by a plasmid gene?

RepA

Which of the following statements is true about the rolling-circle mechanisms of plasmid replication?

RepA nicks one strand of the double-stranded DNA plasmid.

What is the effect of rifamycin on transcription?

Rifamycin binds to the beta subunit of RNA polymerase and blocks the exit channel.

Which of the following is a major advantage of single-cell genomics (SCG) over shotgun sequencing?

SCG requires less sample DNA.

Which of the following DNA repair mechanisms is error prone?

SOS repair

What is the main advantage of scanning probe microscopy as compared to transmission EM or normal scanning EM?

Scanning probe microscopy can be used to view live microbes.

Astrobiologists study the origin of life in the universe and the possibility of life beyond Earth. Which of the following is not a reason why astrobiology involves microbiology?

Scientists are trying to colonize Mars with microorganisms from Earth in an effort to determine whether life can survive on other planets.

How is the small ribosomal unit positioned to allow for translation to start at the proper start codon?

Shine-Dalgarno sequence

Which protein is necessary for extending the linear ends of eukaryotic chromosomes?

Telomerase

How does temperature affect microbial physiology?

Slightly increased temperature speeds up the action of enzymes, thus increasing microbial metabolism.

A local golf course is notorious for using many different chemicals on their grass to get that perfect lawn. Concerns about the effects of these chemicals has led you to sample soils from the golf course and adjacent lots so that you can compare the microbial communities. Which of the following techniques will allow you to separate the culturable species to compare the samples for species richness?

Spread plating serial dilutions of the samples on generalized growth medium

Which of the following sentences is correct?

Sterilization kills all cells, spores, and viruses on an object; disinfection removes pathogens from inanimate surfaces; and antisepsis removes pathogens from the surface of living tissues.

Viruses express tissue tropism and host specificity. In particular, the avian influenza strain H5N1 has rare incidences in humans due to the reduced distribution of alpha-2,3 sialic acids in the lower respiratory tract. As a consequence, when the H5N1 strain does infect a human, the disease is very severe due to the risk of pneumonia. In contrast, human influenza strains (H1N1, among others) attach to alpha-2,6 sialic acids, which are readily expressed in the upper and lower respiratory tract. Which of the following would not be true if a mutation were to allow the H5N1 strain to attach to alpha-2,6 sialic acids?

The avian influenza strain would only infect the lower respiratory tract of humans.

Although Vibrio cholerae is approximately 0.5 µm wide and 1.5 µm in length, filtering water contaminated with Vibrio cholerae through a cloth with 20-µm mesh holes was successful in reducing cholera infections in Bangladesh. Why?

The cloth was able to filter out copepods, which are colonized by Vibrio cholerae.

Why are human eyes not able to use all of the information in visible light?

The distance between photoreceptors is greater than the wavelength of visible light.

Prions are aberrant proteins that cause Creutzfeldt-Jakob disease in humans, mad cow disease from contaminated beef, and scrapie in sheep. Unfortunately, prions have demonstrated the highest resistance to methods of chemical and physical control, including the ability to survive nucleases and UV irradiation. Prions propagate aggregates of prion proteins by altering the normal quaternary conformation of PrPC in the brain. Based on the quaternary structure shown below, which of the following hypotheses could be supported?

The increased presence of beta pleated sheets confers resistance to PrPSc.

Which one of the following is NOT one of Koch's postulates?

The microbe becomes more virulent with each successive host.

Which of the following would allow a disease-causing microbe NOT to adhere to Koch's postulates?

The microbe is found in all patients with a particular disease but also some patients without symptoms.

Select the true statement regarding the relationship between genotype and phenotype.

The phenotype reflects only the portion of the genotype that is expressed.

Scientists define a process as being under circadian control if which of the following criteria are met?

The process's periodicity is maintained despite slight variations in temperature. The process's clock is able to be "reset" by manipulation of the light/dark entrainment cycles. After entrainment, the process is able to "free-run" in the absence of light cues.

How can purified siderophores from one bacterium be used to inhibit the growth of another bacterium?

The siderophores from one bacterium can absorb free iron in the media or surrounding environment, thereby depriving the second bacterium of the needed nutrient.

Plaque assays are notoriously finicky assays, and whether for a bacteriophage or an animal virus, they will require a soft agar overlay. Which of the following best explains the rationale for this approach?

The soft agar overlay prevents the free diffusion of progeny virions to cells.

Why is the viral shunt so important in marine ecosystems

The viral shunt generates dissolved organic and inorganic nutrients that can be used by other organisms.

What would be the effect of water evaporating from a puddle without anything else acting on it?

The water activity would decrease due to an increase in the concentration of dissolved substances.

Ruth E. Ley and collaborators recently cataloged the intestinal microbiomes of identical and fraternal human twins to determine whether any part of the microbiome might be heritable. These researchers concluded which of the following?

There are certain bacterial species that are shared between identical twins, but not fraternal twins; therefore, only part of the microbiome is inheritable.

What is the relationship between osmolarity and water activity?

There is a negative correlation; as osmolarity increases, water activity decreases.

Which of the following is NOT true concerning all plasmids?

They are always linear DNA.

Which of the following statements best describes microbiomes in nature?

They are composed of multiple species, the vast majority of which remain uncultured.

All of the following describe the unique characteristics of eukaryotic chromosomes, except which statement?

They contain regulatory DNA sequences.

If halophiles require high environmental concentrations of salt (NaCl), then why do they have such high intracellular concentrations of potassium?

They keep sodium levels low by replacing it with potassium since sodium can be used for symport with other solutes.

Which of the following is true of prion diseases?

They lead to neurodegeneration.

How do photosynthetic marine microbes affect Earth's atmosphere?

They produce 50% of Earth's oxygen gas (The other half is generated by terrestrial forests.)

While archaea represent only a small percentage of the human microbiome of many individuals, the most abundant methanogen in the human gut, Methanobrevibacter smithii, accounts for about 10% of all anaerobes found in the human colon. Likewise, the abundance of Methanobrevibacter smithii indicates that it is highly stable and inheritable. All of the following are explanations for these observations, except which one?

They reproduce sexually, thus are able to quickly colonize the gut.

Which marine bacteria are as large as the head of a fruit fly?

Thiomargarita namibiensis

An insertion sequence contains a gene for which enzyme?

Transposase

A protein destined for the extracellular space could be translocated there in which of the following ways?

Type I secretion system

Enzymes that can alter DNA supercoiling are called topoisomerases. Identify the following as characteristics of type I topoisomerases or type II topoisomerases and sort accordingly.

Type I: ATP-Independent Cleaves one strand of the DNA double helix Unwinds supercoils Type 2: Introduces supercoils ATP-dependent Cleaves two strands of the DNA double helix

The enzyme photolyase repairs DNA damage caused by

UV radiation

Cell culture methods provide a fruitful avenue to study viral infections in a closed system. This approach, however, is not without limitations. Which of the following is an obstacle to the the propagation of viral strains in cell culture over time?

Virus strains can evolve for tissue culture and no longer be viable for animal research.

which of the following statements are true?

Viruses may limit host population density.

To clearly observe a single bacterium's subcellular structure, the best tool is

a transmission electron microscope

One sign of horizontal gene transfer is

a GC base ratio different from flanking chromosomal DNA.

In the analogy of a computer virus to a biological virus, a personal computer is analogous to

a cell

A mutation always results in

a change in genotype

A pure culture refers to

a culture that contains a single type or strain of microorganism.

Imagine you are investigating a mutant strain of EHEC that is no longer attracted to norepinephrine but still exhibits positive chemotaxis to nutrients such as aspartate, maltose, and galactose. These results would be consistent with which of the following?

a defect in one of the methyl-accepting chemotaxis proteins (MCPs)

An organism that grows best at high osmolarity is called

a halophile

Experiments using twin studies and germ-free mice are providing important insights into the role of the gut microbiome in human health. In a particularly striking example, researchers found that people who carry Christensenella minuta as part of their gut microbiome are more likely to have which of the following?

a lean body mass index (BMI)

The fatty acids found in bacterial phospholipids are

a mix of saturated and unsaturated fatty acids

The protein product of the lacI gene is

a regulatory protein.

An inducer causes gene expression by binding

a repressor protein to remove it from the DNA.

A physician informs a patient that the pathogen that has been causing their infection is a bacillus. When they look at a magnified image of cells from the infection, they see cells of many different shapes and sizes. What shape is the pathogen?

a rod

What is an intein?

a self-splicing protein

CRIPSR is:

a set of short DNA sequences that allow the bacterium to "remember" past infections.

Many alkaliphiles have

a sodium motive force

Assume you are using a microscope that has the ability to provide specific wavelengths of light. Which of the following provides the best minimum resolution distance?

a system using a wavelength of 400 nm with an angle of the light cone being 72° in air

tropism can be defined as

ability to infect a particular type of cell within the host.

For a molecule to fluoresce, it must first ________ light.

absorb

_______ are associated with mine drainage due to their lithotrophic activities.

acidophiles

Which of the following describes a change in an organism's genotype (rather than its phenotype)?

acquisition by Corynebacterium of a prophage that encodes diphtheria toxin

simple stains

add dark color to all cells specifically, improving contrast

viruses infect

all 3 domains of life (bacteria, archaea, and eukaryotes)

Which of the following scenarios would cause a peritrichously flagellated bacterium (like E. coli) to swim in a forward motion?

all flagella turning counterclockwise

Which best describes a genome?

all the genetic information possessed by a cell or virus

culturing viruses in tissue culture

allows for testing of a variety of chemical and biological agents against the virus.

Wet mount preparation of specimens

allows for viewing specimens in as close to the natural state as possible.

Which of the following would not be an advantage to heat-fixing a bacterial specimen to a slide?

allows visualization of flagellar function

During phase variation there is a

alteration of an organism's DNA.

Polar aging can cause members of the population to die as they accumulate damaged proteins at the "old" end of the cell. Some types of cells overcome this issue by

alternating fast and slow extension of the poles.

In a mutant E. coli strain, a protein that normally resides in the inner membrane is mis-localized in the cytoplasm. All other proteins show normal localization. The defect in this strain is that the

amino terminal signal sequence is missing.

Which virus may enter cells via receptor-mediated endocytosis

animal virus

ABC transporters can be efflux transporters that move molecules such as proteases. lipases, and ____ out of the cell

antibiotics

Although the Gram stain provided a tentative identification of C. difficile, which of the following stains would most likely provide the specificity needed to identify the bacteria as C. difficile?

antibody tags

A bacterium produces a toxic metabolic by-product that it needs to efflux to the environment against the toxin's concentration gradient. The energy to drive this efflux comes from the electrochemically favorable influx of protons. This is an example of

antiport

The retractable type IV pilus expressed by the marine bacterium Vibrio cholerae allows uptake of what?

any free double-stranded DNA

A disadvantage of dark-field microscopy is that

any objects in the specimen will scatter light, leading to increased background noise.

Phospholipids with an ether link between glycerol and the fatty acids are found in

archaea

For which organisms would this type of membrane lipid be most adaptive?

archaea in a volcanic hot spring

Pure cultures

are isolated microbial species taken from samples that often contain multiple species.

Archaeans

are prokaryotic like bacteria, but their gene expression machinery is more similar to eukaryotic organisms.

Compared with cellular genomes, viral genomes

are smaller, with fewer base pairs

Viruses cannot be observed using a light microscope because viruses

are too small to resolve using visible light.

Aspirin, like many pharmaceutical drugs, can access the cell because it is a weak acid. This occurs because

as a weak acid it can cross the membrane when in its uncharged form.

Tetracycline is an antibiotic that works by binding to the 30S subunit of bacterial ribosomes, thus inhibiting protein synthesis. This drug is able to cross the cell membrane because

as a weak base, it can cross the membrane in its uncharged form.

CRISPR uses pieces of phage DNA incorporated into the genome

as the source of an RNA that will guide Cas proteins to cleave the foreign DNA.

Permeases, periplasmic nutrient-binding proteins, and membrane-spanning pores (porins) all function to

assist in the uptake of molecules too big or polar to diffuse across lipid bilayers.

Which technique does NOT rely on a beam of electrons or light interacting with the specimen?

atomic force microscopy

Acyl homoserine lactone produced by luxI of Allivibrio fischeri is an example of a(n)

autoinducer.

An essential nutrient is one that

bacteria need for proper growth but cannot make themselves.

Imagine scientists have discovered a new antibiotic that inhibits transcription. To determine which subunit of RNA polymerase holoenzyme (alpha, beta, beta-prime, omega, or sigma) the antibiotic targets, researchers took the approach used to determine that rifamycin targets the beta subunit of RNA polymerase. RNA polymerase subunits were isolated from antibiotic-resistant (R) and antibiotic-sensitive (S) strains of bacteria, mixed in vitro, and tested for transcriptional ability. The results are presented below. Based on the data, which subunit is the target of the antibiotic? RNA polymerase subunit combinations that transcribed in the presence of the antibiotic 1. R - alpha, beta-prime, and sigma mixed with S - alpha, beta, and omega 2. R - beta, beta-prime and sigma mixed with S - alpha and omega 3. R - beta-prime, omega, and sigma mixed with S - alpha and beta RNA polymerase subunit combinations that did not transcribe in the presence of the antibiotic 1. R - alpha and omega mixed with S - alpha, beta, beta-prime, and sigma 2. R - beta, omega, and sigma mixed with S - alpha and beta-prime 3. R - alpha and sigma mixed with S - beta, beta-prime, and omega

beta-prime

Anti-anti-sigma factors

bind anti-sigma factors, releasing sigma factors to activate transcription.

Sigma factors are responsible for

binding of RNA polymerase to consensus sequences on DNA.

Various sigma factors play a role in gene expression by

binding to a variety of different -10 and -35 sequences.

In addition to providing structural support and mediating transport, membrane proteins are important for allowing bacteria to sense and respond to changes in their environment. For example, the ToxR protein is found in the plasma membrane of Vibrio cholerae cells. It responds to pH and temperatures characteristic of the human gut environment by

binding to the promoters of genes involved in virulence.

Green fluorescent protein can be fused to other proteins to visualize them via fluorescence microscopy. If the emitted light is green, what color light may have been used as the excitation wavelength?

blue

Which organisms produce alginate, the substrate for the AguEFG transporter system of the marine microbe Thermotoga maritima?

brown seaweeds

Early microbial ecologists knew that hydrogen gas is oxidized in soil and that ammonia is oxidized in sewage. How did these scientists determine that microbes are responsible for these ecological reactions?

by applying heat and antimicrobial treatment to sewage samples and observing that nitrate was no longer formed

increased synthesis of _____ is a direct result of decreasing glucose levels.

cAMP

The dilution streaking technique is probably the most common procedure performed by microbiologists on a daily basis. It is not, however, particularly useful for

calculating the concentration of viable cells in a culture.

Bright-field microscopy depends on the balance between light and contrast as well as the quality of the lenses used. A(n) __________ microscope compensates for aberrations in the lenses used.

compound light

Which of the following technologies describes how super-resolution imaging can track a single molecule inside of a cell, even though the resolution limit of light is much larger than the molecule being tracked?

computation of central peak position based on intensity profile

Which lens does not magnify an image

condenser

Which type of DNA uptake is dependent on transferable plasmids?

conjugation

AraC is one of a large family of AraC-like proteins. All these proteins

contain a high degree of homology to AraC and XylS.

A DNA site that binds a regulatory protein can be indicated when the DNA

contains an inverted repeat.

Suppose you want to isolate E. coli mutants incapable of synthesizing the amino acid arginine. You grow mutagenized bacteria on a master plate of complete media and make a replica plate (by pressing a velvet block onto the master plate and then pressing it onto the replica plate—bacteria will be transferred) on media lacking arginine. Colonies that grew on the master plate but not the replica plate are arginine-synthesizing mutants. In this example, the replica plate

contains selective media

Quorum sensing

coordinates biofilm formation via chemical signaling among cells.

The amino acid tryptophan functions as a(n) ___ in the control circuit of the trp operon

corepressor

The three-dimensional structure of a virus particle would best be visualized using __________ microscopy.

cyro-electron

Base excision repair is particularly useful for removing bases from DNA that have spontaneously

deaminated

Modern high-intensity electron beams have helped cryo-EM techniques to image the internal ultrastructure of one of the smallest microbes in the ocean, Pelagibacter. What can high-intensity electron beams do that makes them more effective than earlier instruments?

detect smaller structures

The final three-dimensional shape of a protein is

determined by the gene encoding that protein.

All of the following would represent good research applications for cell fractionation except

determining whether a bacterium can metabolize certain sugars.

What is the primary function of ruminant microorganisms? Which of the following would not be considered an endosymbiont?

digestion of cellulose to organic acids intracellular bacteria, such as Mycobacterium tuberculosis, that inhibit macrophage apoptosis

Sergei Windogradsky

discovered chemolithotrophs in natural environments.

Which of the following would have the greatest effect on cell function due to changes in pH?

disrupting protein secondary structure, thus decreasing enzyme activity

The terms "peritrichous," "lophotrichous," and "monotrichous" describe the

distribution of flagella around a bacterium.

Paralogs arise within a genome by which process?

divergence of a duplicated gene

the start of bacterial replication depends on the increase in the concentration of active ____, which accu,ulates during the growth phase of the microbe

dnaA

genomes may comprise

double or single-stranded DNA or double or single-stranded RNA

A paralog is a __________ gene in __________ species, while an ortholog is a duplicated gene in a __________ species.

duplicated; one; two

When could virions (such as T4 phage particles) be detected within an E. coli cell?

during the end of the lytic cycle

The semiconservative nature of DNA replication indicates that

each daughter cell receives one parental strand and one newly synthesized strand.

A new E. coli permease is discovered that moves an uncharged sugar molecule into the cell along with a proton. This new permease can be classified as an

electrogenic symporter

Viruses are most commonly known for infectious diseases such as influenza or measles; however, not all viruses pose harm to the human host, and, in some cases, they can contribute to human survival. Which of the following is an example of the benefits conferred by endogenous viruses?

encoding placental proteins that are essential for early development of human embryos

MacConkey agar is most suitable for the cultivation of which of the following?

enteric pathogens (such as Salmonella and Shigella)

If a bacterial species lacks a cell wall, a reasonable prediction about the environment where this species lives is that it

experiences a constant solute concentration.

Organic farmers use the bacterium Bacillus subtilis to prevent downy mildew in grapes and powdery mildew in greenhouse tomatoes. The farmers are therefore using this bacterium as a _____

fungicide

Which of the following mechanisms do prokaryotes use to generate phase variation?

gene inversions slipped-strand mispairing

Another fundamental discovery provided by André Lwoff and Antoinette Gutman demonstrated that a bacteriophage could integrate itself within the bacterial genome. This was the first recognition that _______ could enter or exit a cellular genome.

genes

Which of the following are two important reasons why microscope lenses are glass parabolas?

glass for refractive index and parabola for bending light rays to intersect at a focal point

A second, outer membrane is found in

gram-negative bacteria

Extremophilic organisms

grow in conditions that would be unable to support human life.

Bacteria, archaea, and eukaryotes all

have double-stranded DNA genomes.

Suppose you were interested in the effect of breastfeeding versus formula feeding on the composition of gut flora in newborns. As part of your experiment, stool samples from healthy babies in the study get plated on various agar media. You notice that greater numbers of colonies are recovered when samples are plated on blood agar compared to Luria Bertani (LB) agar. After some diligent subculturing, you isolate several bacterial species capable of slow growth on the blood but not on the LB agar. You correctly surmise that these organisms

have extensive and complex nutritional requirements not met by LB agar.

Eagles can see smaller objects than humans can because eagle eyes

have higher resolution

Of the following animals, __________ have the sharpest vision due to closely packed __________.

hawks; photoreceptors

Which characteristic of endospores led to confusion when Tyndall tried to replicate Pasteur's experiments regarding spontaneous generation?

heat resistant

Organisms that need to ingest reduced carbon are called

heterotrophs

Pasteurization limits microbial numbers through

high heat

One physical means for killing a psychrophilic bacteria is

high temperature

A steam autoclave attempts to kill bacteria through a combination of

high temperature and high pressure.

Within temperatures allowable for growth, higher temperatures usually lead to

higher growth rates

You have isolated a mutant strain of Bacillus subtilis (which you designate wimP) whose endospores can be killed by boiling water. When you analyze the endospores produced by this strain, you find that compared to endospores produced by the parent (a wild-type strain), the wimP spores have significantly

higher water content

Which of the following pairs make up a classic two-component signal transduction system?

histidine kinase and response regulator

Genes that share a common ancestry are broadly referred to as ______. They are further classified as _________, if they exist within the same species but have distinct functions, while ________ usually have similar functions but are found within different species.

homologs paralogs orthologs

Predicting relatedness of viruses is often very difficult if relying solely on genomic sequences since viruses that share a host can exchange genetic components. This suggests that the ____________ plays a critical role in the evolution of viruses. Along this vein, examining ____________ can demonstrate functional relatedness of viruses that can be obscured in genomic sequences due to mutations and continual exchange of genetic information between co-infecting viruses.

host range proteomics

If a bacterium's cell volume decreases after it is placed in solution A, then solution A is _______ relative to the bacterium.

hypertonic

Analyze the following statements to identify which techniques have similarities to scanning electron microscopy (SEM) for the reason given. i. SEM and differential interference contrast microscopy both provide a 3D image of the cell surface ii. SEM and the Gram stain technique both use multiple treatments with stains, washes, and mordants to view specimen iii. SEM and differential staining both only use one stain iiii. SEM and X-ray crystallography both provide the same level of resolution iiiii. SEM and transmission electron microscopy use the same illumination source (select all that apply)

i. SEM and differential interference contrast microscopy both provide a 3D image of the cell surface iii. SEM and differential staining both only use one stain iiiii. SEM and transmission electron microscopy use the same illumination source

Cellular synthesis of which of the following would be directly affected by nitrogen limitation? i. amino acids ii. simple sugars iii. nucleotides iiii. fatty acids select all that apply

i. amino acids iii. nucleotides

Vascular plants absorb the majority of their essential nitrogen from soil in the form of i. ammonium ii. nitrogen gas iii. nitrite iiii. nitrate

i. ammonium iiii. nitrate

In what ways are wet mount slide preparations disadvantageous when viewing live specimens? i. boils specimen ii. harder to observe live behavior iii. bacteria appear "hollow" iiii. little contrast with external medium iiiii. more artifacts (select all that apply)

i. boils specimen iii. bacteria appear "hollow" iiii. little contrast with external medium

Which of the following would be appropriate for a metagenomics study?

i. hydrothermal vents ii. dental plaque

Which of the following may be present as part of the prokaryotic genome?

i. plasmid ii. prophage iiii. chromosome

In what ways do virions resemble living cells?

i. some virions possess genes for tRNA iii. they posses genes that can direct their own replication iiiii. their genomes can be larger than some cellular genomes

Microbes can develop resistance to chemical control agents

if low concentrations of the chemical are applied to reduce the number of microbes below target number.

Which criteria of Koch's postulates would not necessarily be met when trying to link a particular bacterium to a latent infection, such as tuberculosis or Lyme disease? i. The same strain of microbe is obtained from a newly diseased host. ii. When the microbe is introduced into a healthy, susceptible host, the same disease occurs. iii. The microbe is found in all cases of the disease but is absent from healthy individuals. iiii. The microbe is isolated from the diseased host and grown in pure culture.

ii. When the microbe is introduced into a healthy, susceptible host, the same disease occurs. iii. The microbe is found in all cases of the disease but is absent from healthy individuals.

Which of the following are extragenomic DNA molecules that commonly interact with bacterial genomes?

ii. bacteriophage genomes iii. horizontally transferred bacterial plasmid

What are the components common to all virions? i. DNA and RNA genomes ii. capsid iii. envelope iiii. DNA or RNA genomes

ii. capsid iiii. DNA or RNA genomes

Identify the function(s) of the viral capsid.

ii. determines the shape of the virion iiii. protects the viral genome

The dilution streaking technique can take a bit of practice to master. Which of the following represent sources of error that would likely result in failure to obtain isolated colonies?

ii. flaming the loop immediately after obtaining the bacterial sample iii. forgetting to flame the loop before streaking sequential sections of the plate iiiii. not creating a small section of overlap across sequential sections

Cell biologists studying the mobility of plasma membrane proteins fused mouse and human cells together, creating a heterokaryon. They then examined the localization of mouse and human proteins over time. Initially the mouse and human proteins were restricted to separate halves of the heterokaryon. Over time the mouse and human proteins mixed, with each protein eventually being present over the entire cell surface, consistent with proteins being able to move within the plane of the membrane. What techniques could have been used to examine the locations of the mouse and human membrane proteins? i. fluorescence microscopy with fluorophore-labeled nucleic acids ii. fluorescence microscopy with gene fusion reporters iii. transmission electron microscopy iiii. scanning electron microscopy iiiii. fluorescence microscopy with fluorophore-labeled antibodies (select all that apply)

ii. fluorescence microscopy with gene fusion reporters iiiii. fluorescence microscopy with fluorophore-labeled antibodies

Which of the following are associated with X-ray diffraction analysis? i. induces mutations in microbial specimens ii. is based on the principle of wave interference iii. requires formation of pure crystals of specimens iiii. allows visualization at an atomic level iiiii. does not destroy specimens so it can be used for other studies (select all that apply)

ii. is based on the principle of wave interference iii. requires formation of pure crystals of specimens iiii. allows visualization at an atomic level

Florence Nightingale's statistical analysis of the leading causes of mortality of British soldiers convinced the British government to do all the following except i. improve the ventilation systems in army hospitals and soldiers' living areas. ii. supply soldiers with additional weapons and ammunition. iii. improve the quality of water delivered to soldiers. iiii. improve the standards of army hospitals.

ii. supply soldiers with additional weapons and ammunition.

Which of the following is NOT a reason microbes can be difficult to classify? i. they can exchange genes in non-sexual ways ii. their DNA is easily acquired, amplified, and compared using modern techniques iii. they are difficult to distinguish using microscopy or culture iiii. as asexual organisms, the species concept does not apply to them

ii. their DNA is easily acquired, amplified, and compared using modern techniques

Bacteria exposed to quinolone-type antibiotics rapidly become unable to i. synthesize peptidoglycan ii. maintain ion gradients across the membrane iii. condense and package their chromosomes iiii. replicate their DNA iiiii. translate RNA into protein iiiiii. carry out normal gene expression (select all that apply)

iii. condense and package their chromosomes iiii. replicate their DNA iiiiii. carry out normal gene expression

MacConkey agar is an example of a medium that is which of the following?

iii. differential based on ability to ferment lactose iiiiii. selective for gram-negative bacteria

Which of the following would be positively identified by an acid-fast stain? i. escherichia coli ii. proteobacteria iii. mycobacterium iiii. bacteroidetes iiiii. clostridium difficile iiiiii. enterococcus faecalis iiiiiii. firmicutes (select all that apply)

iii. mycobacterium

Which of the following would Gram stain negative? i. mycobacterium paratuberculosis ii. enterococcus faecalis iii. proteobacteria iiii. escherichia coli iiiii. bacteroidetes iiiiii. firmicutes iiiiiii. clostridium difficle (select all that apply)

iii. proteobacteria iiii. escherichia coli iiiii. bacteroidetes

Microbes have shaped human history by i. being important in the production of certain food products ii. being the causative agents of human epidemics iii. playing important roles in the geochemical cycling of many elements iiii. all of these answer choices are correct

iiii. all of these answer choices are correct

Rolling-circle replication of plasmids proceeds

in one direction from a single fixed origin.

Put the following events in order as they occur during the response of E. coli to a chemical attractant.

in the absence of attractant, CheA is active CheA activity produces high levels of CheY-P CheY-P causes clockwise rotation of flagella (tumbles) Attractant binds and decreases CheA activity Low levels of CheY-P result from CheZ and low CheA activity flagella turn counterclockwise (run)

If the deoxyadenosine methylase (dam) enzyme is inhibited in E. coli, then the next generation time will

increase due to more persistent SeqA binding.

What accounts for the rapid increase in Aliivibrio fischeri autoinducer after the threshold concentration has been reached?

induction of luxI by LuxR

Riboswitches are RNA molecules that can

inhibit translation by preventing access to the ribosomal binding site.

Sigma factors are necessary in which phase of transcription?

initiation

Tetracycline binding is most similar to that of which of the following?

initiation factor 1 (IF1)

Which of the following bind regulatory proteins involved in transcriptional control?

inverted repeats

The pH of the environment can affect microbial growth because

ionizable functional groups of the proteins inside the cell can be protonated or deprotonated, changing the protein's shape.

Initiation of DNA replication in a bacterial species

is influenced by environmental factors.

What would most likely happen to a periplasmic protein in the general secretion pathway if the gene sequence is modified and the N-terminal sequence is significantly shortened?

it will be defective in binding SecB it will not be cleaved by LepB

The chemotaxis protein CheA in E. coli is an example of a protein​​​​​​​

kinase

Which of the following is a unique characteristic of viruses that distinguishes them from the other major groups of microorganisms?

lack of cell structure

Genes can be lost during genomic evolution through

lack of repair to the gene when it is no longer needed.

In the basic Ames test for mutagenesis, a mutagen is tested to see if it can produce colonies on basic medium that ______ histidine, starting with a _____ strain of bacteria.

lacks; hisG mutant

In order to resolve spherical bacteria 1 μm in diameter,

light of a wavelength less than 1 μm must be used.

Reports of disease caused by enteropathogenic E. coli and its relative, Salmonella, usually include a description of the responsible serotype. For example, in 1993, hundreds of infections from Shiga-toxin-producing E. coli resulted from undercooked hamburgers sold by Jack-in-the-Box restaurants. The outbreak was caused by the now-infamous E. coli strain O157:H7. The "O" in this designation refers to an antigen on which of the following molecules?

lipopolysaccharide

The "rock-eating" bacteria are typically known as

lithotrophs

Spontaneous generation is the notion that

living organisms arise from nonliving matter

The role of the DnaC protein in replication is to

load helicase

Temperate bacteriophages can undergo two routes of infection. During _________ the phage DNA is inserted into the bacterial genome and replicated each time the bacterial cell divides.

lysogeny

The temperature phage lambda can undergo two life cycles depending on the environmental cues. During which cycle does phage lambda form a prophage?

lysogeny

A _____ virus cycle leads only to cell lysis, and a _____ virus cycle involves phage genome integration into the host genome.

lytic; lysogenic

supercoiling of DNA

may be affected by antibiotics

The surface layer (S-layer) of prokaryotes

may be lost from bacteria cultured in the lab.

Compared with cells that are surrounded by a lipid membrane, viruses

may be surrounded by a membrane derived from the host cell.

biofilms

may cause health problems for humans.

Over time, the genome of a species

may change due to mutation or gene exchange.

Transposable elements differ from plasmids in that only plasmids

may exist autonomously, not integrated into host DNA.

Which of the following would be the best way to determine the effect of promoter mutations on transcription?

measure specific mRNA expression

A raindrop of almost pure water lands on a microbe. Which housekeeping strategy, activated by osmotic pressure, is used by microbes to reduce their internal solute concentration by letting solutes out?

mechanosensitive channels

Most human pathogens prefer temperatures similar to

mesophiles

The collection of sequences sampled from a particular environmental sample is called

metagenome

Eutrophication may lead to decreased

microbial diversity

Choose the pair of words that correctly completes the following sentence: Biofilms preferentially form in __________ environments with __________ levels of nutrients.

moist/ high

Which of the following organisms are not considered microbes?

mosquito

The statement "codons are redundant" refers to the fact that

most amino acids are specified by more than one codon.

By exposure to low concentrations (non-lethal doses) of triclosan, bacteria may become resistant. Some mechanisms of triclosan resistance may also enable the bacterium to be resistant to multiple antibiotics. Order the following mechanisms from most likely to least likely to confer cross-resistance to antibiotics. In other words, rank these events from conferring more broad-spectrum resistance to less broad.

most likely acuisition of efflux pumps modification of the outer membrane to lower triclosan permeability altering the fatty acid synthesis protein (fabI) targeted by triclosan least likely

halophiles

must have 10%-20% NaCl levels to grow.

A(n) ________ is one-millionth of a millimeter

nanometer

in most bacterial species the DNA is

negatively supercoiled.

A bacterial pathogen that can cause septicemia (infection of the blood) is likely a(n)

neutralophile.

A continuous culture differs from a batch culture because in continuous culture,

new medium is added and old culture removed.

which statement concerning the genomes of organisms is true

organisms differ in their genome size

The heterocyst cells of cyanobacteria are specialized for

nitrogen fixation

The reduction of N2 gas into ammonia is known as

nitrogen fixation

Nitrogen fixation is the conversion of

nitrogen gas to ammonium ions.

A single base-pair mutation occurs in a promoter sequence of a gene. As a result of the mutation, what are the possible effects on the transcription level of the gene?

no effect increase reduction elimination

Eukaryotic genomes comprise mostly __________, whereas prokaryotes have mostly __________.

noncoding DNA; coding DNA

Based on gel electrophoresis, a nonfunctional protein is found to have a smaller molecular weight than its wild-type counterpart. A likely explanation for this observation is a

nonsense mutation in the DNA coding for the protein.

An E. coli strain with a mutation rate of about 10-10 per base pair replicated would be considered a ___ strain

normal

Consider the data from a hypothetical Ames test below. Then match the following chemicals to the best description of their mutagenicity: mutagenic to bacteria only, mutagenic to both humans and bacteria, or not mutagenic at all.

not mutagenic : monosodium glutamate (MSG) Bacteria only: caffeine humans and bacteria: tobacco smoke the fatty acid 4-hydroxyhexenal

One form of genome organization in a bacterial cell is the compartmentalization of chromosomes and plasmids. When bacterial chromosomes and plasmids are fluorescently labeled in vivo, chromosomes are consistently localized to the __________ and plasmids are consistently localized to the __________

nucleoid cel poles

The major factor limiting bacterial growth in nature is

nutrients

The nosepiece of a compound microscope contains

objective lenses

The stringent response

occurs in response to low energy stores.

Organisms with a high rate of growth at low nutrient concentrations are called

oligotrophs

the transformed focus assay is used for ____ viruses

oncogenic

Chemolithotrophs

only grow in inorganic solutions rather than organic media.

A(n) __________ is composed of DNA.

operator

Bacteria may donate DNA to other bacteria of the same

or of a different species, some eukaryotic cells, and bacteriophages.

Bacterial replication begins at a single, defined DNA sequence known as _____

oriC

The covalent attachment of an acetyl group to a protein is an example of

posttranslational modification.

In metagenomics, a "core gene family" is one that is

present in at least some members of all communities examined.

A woman with irritable bowel syndrome attempts to restore normal intestinal microflora by ingesting yogurt containing live, active cultures. This is an example of using

probiotics

Penicillin is

produced by a mold and was discovered accidentally

Within the order of viruses called Caudovirales is a/an __________ that possesses a thin filamentous tail used to infect Staphylococcus aureus. Since Caudovirales viruses encode virulence factors such as Panton-Valentine leukocidin, which allows bacterial escape from leukocytes, this virus and bacteria have formed a/an __________ relationship.

prophage mutualistic

Some bacteria, such as salmonella, use a _____ to regulate the half-lives of sigma factors during different stages of growth.

protease

Before the scientific advances of the mid-20th century, most scientists believed that a cell's genetic information was encoded by

protein

The viral capsid is comprised of

proteins

viroids lack

proteins

The phylogenetic tree of Prochlorococcus suggests that early lineages lived deeper in the euphotic zone below the limit of UV light penetration. What DNA repair adaptation currently allows Prochlorococcus cells to live in the upper photic zone?

protolyases

Which of the following is a mechanism used to store energy for later use in bacterial cells?

proton motive force

Aspects of microbial physiology that can be affected by changes in temperature include all the following EXCEPT

protonation of enzymes

In addition to the psychrophiles commonly found in the Antarctic, the other types of microbes usually found there are ____ sin e they can handle the conditions that are present in that environment

psychotropic

In a proper Gram stain, Gram-positive cells appear _______________ in color.

purple

Yersinia pestis, the main causative agent of bubonic plague, was transmitted by

rat fleas

the role of the DnaA protein in replication is to

recognize the oriC sequence and initiate replication.

RNAi

recognizes viral mRNA and prevents further viral gene expression.

Agar is extracted from

red algae

The characteristic of light that allows magnification by a microscope is

refraction

Most known sRNAs are responsible for

regulating protein levels at the level of translation.

Alternative sigma factors are important for controlling expression of

regulons necessary for surviving adverse growth conditions.

All cells are made up of water and essential ions as well as small and large organic molecules. Order the following components in E. coli during balanced exponential growth from greatest to least in terms of percentage of total cellular weight.

relative total weight (greatest) water protein nucleic acid (DNA and RNA) lipids inorganic ions (least)

For the mismatch repair system to work correctly, newly replicated DNA must

remain unmethylated long enough for mismatches to be repaired. become methylated before the subsequent round of replication.

Archaea are prokaryotic cells, yet based on the comparative analysis of ________________, archaea are more closely related to eukaryotes than to bacteria.

ribosomal RNA (rRNA) sequences

Guanosine tetraphosphate (ppGpp) serves as a signal to the cell that

ribosome synthesis should be curtailed.

Why might regulation by sRNA be considered more energetically efficient than regulation by repressors?

sRNAs do not need to be translated.

Many bacteria adapt to adverse environmental conditions by modifying the composition of their cell membranes. For example, the membranes of bacteria subjected to heat stress often contain high levels of which of these compounds?

saturated fatty acids

The best microscope technique for observing the arrangement of different proteins of the surface of bacteria is

scanning electron microscopy.

Bacterial cultures appear cloudy because of the _______________ of light.

scattering

Dark-field microscopy depends on which characteristic of light?

scattering

Helicobacter pylori is a causative agent of gastric ulcers. It survives in the low pH environment of the stomach by

secreting urease to generate ammonia.

In a two-component signal transduction system, the __________ senses a change in the environment and the __________ changes gene expression.

sensor response regulator

Which of the following transcriptional control elements covalently modifies its target?

sensor kinases

early microscopes

showed cells in living material

Tomato mosaic virus (ToMV) causes significant economic losses in agriculture and food crops. ToMV is not only a problem for tomatoes; it can also impact peppers, potatoes, apples, and cherries. Upon infection, the virus causes the plants to yellow and have stunted growth and reduced yield. Fortunately, similar to humans, plants have adapted defenses to survive viral onslaughts. The discovery of ________ in plants has led to a deeper understanding of how cells protect themselves from stress responses and, of course, viral infections.

siRNA for RNA interference

With respect to controlled protein degradation,

signals called degrons dictate the stability of a protein.

Bacteria have higher D-values for irradiation than protists because bacteria have

smaller genomes

Resolution refers to which of the following?

smallest distance by which two objects can be separated and still be distinguished as separate

To maintain water balance in a hypertonic environment, some microorganisms accumulate intracellular solutes. Which molecule would NOT be used as a cytoplasmic solute?

sodium ion

the enzyme reverse transcriptase (RT) is found in

some DNA and some RNA viruses

Antibiotics are

sometimes overprescribed.

Which of the following is an advantage of electron microscopy?

specimens can be observed at higher resolution

Which of the following criteria is not part of the International Committee on Taxonomy of Viruses (ICTV) classification system?

spike proteins

Which of the following bacterial shapes is believed to have evolved only once?

spirochete

The theory that organisms can arise from inanimate matter is called

spontaneous generation

What induces intein splicing in Pyrococcus horikoshii RadA?

ssDNA

Aerobes may tolerate the presence of oxygen because they have the enzyme

superoxide dismutase

Proteins have optima for

temperature, pHm and osmolarity

The idea that the bacterial genome is "loose" in the cytoplasm is incorrect because

the DNA is attached to the cell envelope and organized into domains through supercoiling and DNA-binding proteins.

Choose the best definition of metagenome.

the collective genes from organisms within a given microbiome

The Baltimore classification of viral genomes is based on

the composition of the genome.

Which of the following is the best example of an extremophile?

the hyperthermophile bacteria Methanopyrus kandleri

The term "phage therapy" refers to

the idea that phages could be used to treat bacterial diseases.

Suppose a bacterium was exposed to a chemical that poisoned its cytochrome oxidase. Which of the following transport processes would be affected first?

the lactose symporter (LacY)

The "coding region" of a gene corresponds to which?

the nucleotides that specify the amino acid sequence of a protein

a specific virus always infects

the number of species depends on the virus

In the plaque assay for bacteriophages

the plaque is a clear zone caused by a zone of lysis.

Which of the following techniques would be best to use to study extremophiles that cannot be cultured in normal laboratory conditions?

the polymerase chain reaction to amplify the DNA to have enough for further analysis

Caulobacter crescentus has asymmetrical cells, where one pole is plain and the other can have either a flagellum or a stalk. The difference between the poles is

the presence of a protein marker TipN marking the pole for a cellular extension.

Antibiotic resistance in Mycobacterium tuberculosis is a global health concern. It can arise very rapidly in this microbe because

the process of cell division produces cells of varying age classes, each having different structural and metabolic properties, allowing different cells in the population to be resistant to different antibiotics.

Why is it incorrect to refer to conjugation as bacterial sex?

the recipient is haploid for the transferred genes it does not involve gametes the transferred DNA is not required for normal cellular function

E. coli is a barosensitive organism. How does high pressure affect E. coli ribosomes?

the ribosomes dissociate

Denaturation of DNA refers to

the separation of the double helix into single strands.

Empty magnification occurs when

the size of an image increases with no increase in resolution.

In microscopy, the term "resolution" refers to

the smallest distance by which two objects can be separated and still be distinguished.

in bright-field microscopy

the specimen absorbs light and appears dark.

Distortion when using a light microscope at the highest levels of magnification is decreased by

the use of immersion oil.

Bacteria as a group are incredibly metabolically diverse, but individual species are often highly specialized to reduce competition in their natural environment. This results in these species being unculturable because

their growth may depend on necessary growth factors provided by other organisms in their natural environment.

The 30S and 50S ribosomal subunits are so designated to indicate

their sedimentation rate in a centrifuge.

Which of the following is true of viruses?

they are not cells

How are matthew sullivan and his colleagues able to link viruses to the hosts they infect?

they connect virus genome data with host-cell genome data

Which of the following directly describes where the name ABC transporters comes from?

they have nucleotide binding domains

The prokaryotic ribosome consists of

three RNAs and many proteins.

Membranes prevent movement of most substances between the cell and the environment, but most required substances can be moved

through proteins embedded in the membrane that "recognize" specific substrates and allow their passage.

Carl Woese proposed the domain classification

to account for two major and distinct prokaryotic groups in addition to eukaryotes.

For what purpose does the bobtail squid (Euprymna scolopes) use the light produced by its symbiotic A. fischeri?

to avoid predation

biofilms form

to establish a collaborative community that promotes the members' growth and reproduction.

Most species of bacteria cannot be eaten by humans because the bacteria contain

toxic levels of nucleotides.

DNA is __________ into mRNA and mRNA is _________ into proteins.

transcribed translated

Which type of DNA uptake is dependent on viruses?

transduction

Consider the descriptions of genetic exchange methods below and match each description to the proper type of exchange.

transduction: This method can occur with cell-free extract only and is not affected by DNase. conjugation: This method of DNA exchange cannot occur using the recipient cells mixed with cell-free extract only. transformation : This method would be affected by DNase, an enzyme that can degrade naked DNA that is unprotected.

The process of importing free DNA from the environment into cells is called

transformation

Which mechanism of gene transfer among microbes was elucidated by the team of Avery, MacLeod, and McCarty?

transformation

Which of the following is an example of horizontal transmission?

transformation

One advantage to using sRNAs to control protein expression is that

translation of the sRNA is not needed, thus saving amino acids.

Secondary chromosomes most likely evolve in bacteria as a result of

translocation of one or more essential genes from the primary chromosome to a resident plasmid.

active transport is required for bacterial cells to

transport solutes against their concentration gradient

What are the basic parts of an insertion sequence?

transposasae coding region two flanking inverted repeats

Many barophiles are also psychrophilic because it is

usually cold at the ocean depths.

A viral genome was one of the first genomes sequenced because

viral genomes are relatively small.

RNA retrovirus use

viral reverse transcriptase to make a DNA copy that is integrated into the host genome and then host RNA polymerase transcribes it.

Viruses are capable of converting into a(n)

virion, an intracellular replication complex, and an integrated part of the host genome.

In 1899, Beijerinck found that the infectious agent of tobacco mosaic disease went through a filter of 0.1μm pore size. Stanley later purified and crystallized the infectious agent from infected tobacco leaves. The infectious agent was found to be a(n)

virus

Gene transfer agents, when viewed using electron microscopy, could easily be mistaken for

viruses

which of the following may possess an RNA genome

viruses

What key feature of marine viruses drives biodiversity in the oceans?

viruses have very limited host ranges

Culturing viruses in a laboratory is more complicated than culturing bacteria because

viruses must be cocultured with a host cell.

Compared with the number of antibiotics, the number of antiviral drugs is small because

viruses use host cell machinery to replicate.

chemical imaging microscopy

visualizes the distribution of chemicals in a sample using mass spectrometry.

The most abundant molecule in the cell is

water

Under what condition would a temperate bacteriophage infecting Staphylococcus aureus (an aerobic bacteria commonly found on the human body) be shifted by environmental cues from lysogeny to a lytic cycle?

when phage-infected cells are placed on nutrient-rich media

Cell fractionation provides information about the following EXCEPT

whole-cell function

Glucose uptake against a bacterium's concentration gradient

will require a glucose transport protein and will also expend energy.

There are only about 40 different tRNAs in a cell even though 61 codons code for amino acids. This discrepancy can be attributed to the fact that the first nucleotide in the anticodon can base-pair with more than one nucleotide in the codon. This phenomenon is known as __________ and is, in part, due to __________ and the presence of __________ at this position in some tRNA molecules.

wobble; the curvature of the anticodon loop; inosine

Which technique requires prior crystallization of the specimen?

x-ray diffraction analysis

A strain of Mycobacterium tuberculosis that is deficient in nonhomologous end joining repair should be more sensitive to damage by _________

x-rays

While adding nutrients to a culture medium in a glass container, which of the following would LEAST likely need to be added?

zinc